>> Use local variable to bdrv_pwrite_sync L1 table,
>> needless to make conversion of cached L1 table between
>> big-endian and host style.
>>
>> Signed-off-by: Zhang Haoyu <zhan...@sangfor.com>
>> ---
>> v1 -> v2:
>> - remove the superflous assignment, l1_table = NULL;
>> - replace 512 with BDRV_SECTOR_SIZE, and align_offset with ROUND_UP
>> - remove needless check of if (l1_table) before g_free(l1_table)
>>
>> block/qcow2-refcount.c | 24 +++++++-----------------
>> 1 file changed, 7 insertions(+), 17 deletions(-)
>>
>> diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
>> index 2bcaaf9..29a916a 100644
>> --- a/block/qcow2-refcount.c
>> +++ b/block/qcow2-refcount.c
>> @@ -881,14 +881,17 @@ int qcow2_update_snapshot_refcount(BlockDriverState
>> *bs,
>> {
>> BDRVQcowState *s = bs->opaque;
>> uint64_t *l1_table, *l2_table, l2_offset, offset, l1_size2;
>> - bool l1_allocated = false;
>> int64_t old_offset, old_l2_offset;
>> int i, j, l1_modified = 0, nb_csectors, refcount;
>> int ret;
>>
>> l2_table = NULL;
>> - l1_table = NULL;
>> l1_size2 = l1_size * sizeof(uint64_t);
>> + l1_table = g_try_malloc0(ROUND_UP(l1_size2, BDRV_SECTOR_SIZE));
>
>I'm sorry, but I just now realized that we don't even need the 0 variant
>here. We are never accessing any element beyond l1_table[l1_size - 1],
>and all elements from 0 until l1_size - 1 are overwritten by
>bdrv_pread() or memcpy(). Therefore we can simply use
>qemu_try_blockalign(bs->file, l1_size2) here.
>
OK, I will replace g_try_malloc0(ROUND_UP(l1_size2, BDRV_SECTOR_SIZE)) with
qemu_try_blockalign(bs, ROUND_UP(l1_size2, BDRV_SECTOR_SIZE)).
>(and we should be using qemu_{try_,}blockalign() instead of
>g_{try_,}malloc{0,}() whenever possible for performance reasons)
>
>> + if (l1_size2 && l1_table == NULL) {
>> + ret = -ENOMEM;
>> + goto fail;
>> + }
>>
>> s->cache_discards = true;
>>
>> @@ -896,13 +899,6 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
>> * l1_table_offset when it is the current s->l1_table_offset! Be
>> careful
>> * when changing this! */
>> if (l1_table_offset != s->l1_table_offset) {
>> - l1_table = g_try_malloc0(align_offset(l1_size2, 512));
>> - if (l1_size2 && l1_table == NULL) {
>> - ret = -ENOMEM;
>> - goto fail;
>> - }
>> - l1_allocated = true;
>> -
>> ret = bdrv_pread(bs->file, l1_table_offset, l1_table, l1_size2);
>> if (ret < 0) {
>> goto fail;
>> @@ -912,8 +908,7 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
>> be64_to_cpus(&l1_table[i]);
>> } else {
>> assert(l1_size == s->l1_size);
>> - l1_table = s->l1_table;
>> - l1_allocated = false;
>> + memcpy(l1_table, s->l1_table, l1_size2);
>> }
>>
>> for(i = 0; i < l1_size; i++) {
>> @@ -1055,13 +1050,8 @@ fail:
>> }
>>
>> ret = bdrv_pwrite_sync(bs->file, l1_table_offset, l1_table,
>> l1_size2);
>> -
>> - for (i = 0; i < l1_size; i++) {
>> - be64_to_cpus(&l1_table[i]);
>> - }
>
>But I realized something even more important as well: If you are
>modifying the current L1 table, you need to copy the result back to
>s->l1_table.
>
My fault.
>Sorry for having missed these in my previous review.
>
>Max
>
>> }
>> - if (l1_allocated)
>> - g_free(l1_table);
>> + g_free(l1_table);
>> return ret;
>> }
>>
